JP2003191274A - Method for foam molding of thermoplastic resin and foamed molded object - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamed molded object having both of lightweight properties and strength due to fine foaming by putting the maximum cell diameter of air bubbles in a specific range. <P>SOLUTION: In the method for the foam molding of a thermoplastic resin constituted so as to foam the thermoplastic resin mixed with a supercritical fluid in a mold, a filling process of filling a mold preliminarily brought to predetermined pressure by the supercritical fluid with the thermoplastic resin mixed with the supercritical fluid, and a foaming process of lowering the pressure in the mold when the dynamic viscoelastic value of the thermoplastic resin in a solid state below the melting point of the thermoplastic resin in within a predetermined range to start the foaming of the thermoplastic resin and stopping the foaming thereof to obtain the foamed molded object, are performed successively. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam molding method and a foam molded article of a thermoplastic resin, and more particularly to a foam molding method and a foam molded article of a thermoplastic resin mainly using a supercritical fluid as a foaming agent.

[0002]

2. Description of the Related Art A foamed molded article of a thermoplastic resin has hitherto been manufactured using a chemical or physical foaming agent.

[0003] In the production method using a chemical foaming agent, generally, a raw material resin and a low molecular weight organic foaming agent which decomposes at a molding temperature to generate a gas are mixed and heated to a temperature above the decomposition temperature of the foaming agent. In this method, the raw material resin is melted and the gas is generated by the decomposition of the foaming agent to perform foam molding.

On the other hand, in the production method using a physical foaming agent, a low boiling point organic compound such as butane, pentane or dichlorodifluoromethane is supplied to a molten resin under pressure, and after kneading,
It is a method of foaming by discharging into a low pressure region.

However, in the manufacturing method using these chemical or physical foaming agents, the foam cells are made finer and the cell density is increased.
Uniform dispersion is generally difficult. Therefore, the foam obtained by the manufacturing method using these chemical or physical foaming agents has a problem that the mechanical strength becomes relatively low.

Therefore, miniaturization of cells and high density of cells
In order to achieve uniform dispersion, Japanese Unexamined Patent Publication No. 10-230528 and Japanese Patent No. 2625576 disclose a method of using a supercritical fluid as a foaming agent. In this foam molding method, a supercritical inert gas as a supercritical fluid is dissolved in a molten resin in a sufficiently uniform manner, and this is injected and filled into a cavity of a molding die while applying pressure, and then the pressure in the die is rapidly increased. The foamed molded product is obtained by foaming by reducing the amount to 1.

In this foam molding method, it is possible to utilize the excellent solubility of a supercritical fluid, which is close to that of a liquid, and the excellent diffusivity of a supercritical fluid, so that the supercritical fluid can be impregnated into a resin in a short time. Becomes For this reason, it becomes possible to reduce the diameter of the foamed cells, and it is possible to prevent deterioration of the strength and physical properties of the foamed product.

[0008]

By the way, in the conventional foam molding method using the supercritical fluid disclosed in the above publication, the average cell diameter is mainly specified for the cell size.

However, in reality, the starting point of internal defects in strength is the maximum cell diameter portion. Therefore, reliable identification of the physical properties in terms of strength cannot be obtained only by specifying the average cell diameter.

On the other hand, the weight reduction, which is a merit of foaming, may be disadvantageous if it is made too fine.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a foamed molded article that has a maximum cell diameter of bubbles within a specific range and has both weight reduction and strength due to fine foaming. This is a technical issue that should be addressed.

[0012]

A thermoplastic resin foam molding method of the present invention which solves the above-mentioned problems is a method of foaming a thermoplastic resin mixed with a subcritical or supercritical fluid in a molding die. In the foam molding method, in the molding die pre-pressurized to a predetermined pressure by the subcritical or supercritical fluid, a filling step of filling the thermoplastic resin mixed with the subcritical or supercritical fluid, and the heat When the dynamic viscoelasticity value in the solid state below the melting point of the plastic resin is within a predetermined range, the pressure in the molding die is reduced to start foaming of the thermoplastic resin, and the foaming is terminated,
It is characterized in that a foaming step of obtaining a foamed molded article is carried out in order.

In a preferred embodiment, the subcritical or supercritical fluid is carbon dioxide, and the predetermined range of the dynamic viscoelasticity value is 0.07 to 0.1.

In a preferred embodiment, after the foaming step,
A demolding step of demolding the foamed molded product from the molding die is performed when the dynamic viscoelasticity value deviates from the predetermined range.

In a preferred embodiment, the thermoplastic resin is filled in the mold through a hot runner having opening and closing means at the inlet and the gate in the filling step, and the opening and closing means includes at least the mold. Opening and closing control so that the pressure in the hot runner is maintained when the mold is opened, and that it is opened when the thermoplastic resin is filled and at least closed when the mold is opened. To be done.

The foamed molded article of the present invention for solving the above-mentioned problems is a foamed molded article obtained by foaming a thermoplastic resin mixed with a supercritical fluid in a molding die, and has a maximum cell diameter of 0. It is characterized in that it is 5 to 20 μm.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The method for foam-molding a thermoplastic resin of the present invention comprises foaming a thermoplastic resin mixed with a subcritical or supercritical fluid in a molding die, which comprises a filling step and a foaming step. Are carried out in order.

Carbon dioxide, nitrogen or the like can be used as the kind of the subcritical or supercritical fluid.

Here, in the subcritical or supercritical fluid, in addition to the fluid in which both the pressure and the temperature exceed the critical point and are kept in the critical state, one of the pressure and the temperature exceeds the critical point. Fluid that is held at a pressure or temperature that is close to the critical point and the other is a fluid that is held at a pressure or temperature that is close to the critical point, and that is supercritical. Also included are so-called subcritical fluids that can exhibit properties substantially equivalent to those of fluids.

When comparing carbon dioxide and nitrogen,
Since nitrogen has a lower foaming pressure than carbon dioxide, when mixed with the thermoplastic resin at the same gas content, the foamed cell diameter becomes smaller when nitrogen is used.

Further, as the kind of the thermoplastic resin,
Although not particularly limited, for example, polypropylene (PP),
Polyamide (PA6, PA66, etc.), glass fiber-containing polyamide (PA6GF30, etc.), polystyrene (P
S), acrylic acid resin, acrylonitrile-butadiene-styrene copolymer resin (ABS), polyvinyl chloride (P
VC), polycarbonate (PC), polyacetal or polysulfone (PSF) can be used.

In the filling step, the thermoplastic resin in which the subcritical or supercritical fluid is mixed is filled in the molding die which is pre-pressurized to a predetermined pressure by the subcritical or supercritical fluid. That is, by supplying a subcritical or supercritical fluid gas into the molding die to maintain a predetermined pressure in the molding die in advance, while suppressing foaming of the thermoplastic resin mixed with the subcritical or supercritical fluid. The molding die is filled with a thermoplastic resin mixed with a subcritical or supercritical fluid.

The subcritical or supercritical fluid is mixed into the thermoplastic resin in the injection barrel of the injection molding machine before the molten resin of the thermoplastic resin is injected into the mold and filled. That is, in the injection barrel of the injection molding machine,
A subcritical or supercritical fluid is supplied to a molten resin of a thermoplastic resin. By doing so, the supercritical fluid can be rapidly and sufficiently kneaded and dissolved in the thermoplastic resin.

Here, the mixing amount (gas content) of the subcritical or supercritical fluid into the thermoplastic resin affects the foam cell diameter and cell density of the obtained foam molded article. If the gas content is too high, the maximum cell diameter is enlarged and it becomes difficult to secure a predetermined strength. Therefore, for example, when carbon dioxide is used as the subcritical or supercritical fluid, the gas content is preferably 10 wt% or less (not including 0 wt%). On the other hand, if the gas content is too low, the cell density is lowered, and it becomes difficult to obtain a predetermined weight reduction effect. Therefore, for example, when carbon dioxide is used as the subcritical or supercritical fluid, the gas content is preferably 0.2 wt% or more.

In the foaming step, when the dynamic viscoelasticity value in the solid state below the melting point of the thermoplastic resin is within a predetermined range, the pressure in the molding die is reduced to foam the thermoplastic resin. A foam molded body is obtained by starting and ending. At this time, it is preferable to reduce the pressure in the molding die in a short time to start the foaming of the thermoplastic resin and to finish the foaming quickly. Specifically, it is preferable to instantly reduce the pressure in the molding die to the atmospheric pressure to start foaming the thermoplastic resin and finish it within a few seconds. By doing so, cell growth can be suppressed more reliably.

Thus, when the dynamic viscoelasticity value in the solid state below the melting point of the thermoplastic resin is within the predetermined range, the pressure in the molding die is lowered to start foaming of the thermoplastic resin, Moreover, by completing the process, the obtained foamed molded product can be finely foamed, and the maximum cell diameter of the bubbles can be kept within a specific range.
This is because cell growth (speed) can be suppressed by viscoelasticity of resin in which gas is dissolved. When the foaming of the thermoplastic resin is started at a temperature equal to or higher than the melting point of the thermoplastic resin, the cell growth (velocity) rapidly progresses so much that only a foam having a large cell diameter can be obtained.

For example, carbon dioxide is used as the subcritical or supercritical fluid, the predetermined range of the dynamic viscoelasticity value is 0.07 to 0.1 as described later, and the gas content rate with respect to the thermoplastic resin is, for example. When the amount is 10 wt%, in the obtained foamed molded article, as shown in FIG. 1, the maximum cell diameter of bubbles can be set in the range of 0.5 to 20 μm.
The measurement of the dynamic viscoelasticity value was performed using a measuring device manufactured by Rheometrics, Inc., and the test piece shape was t3.2 × 10 ×.
It was carried out under the conditions of 30 mm, temperature rising rate: 2 ° C./min. Also,
The maximum cell diameter was determined by measuring the maximum foamed cell diameter in a 500 μm square photograph taken by a scanning electron microscope at any 5 cross-sections of the molded product. In addition, the gas content is the total weight of the sample before adding the gas, immediately after cooling the gas-dissolved sample into the resin by rapidly cooling it to room temperature without trapping it and confining the gas in the resin. Calculated from the ratio.

Thus, the lower limit of the maximum cell diameter is 0.5 μm.
If so, it is a region where the effect of weight reduction due to foaming is exhibited in an actual product by 5% or more. Further, when the upper limit of the maximum cell diameter is 20 μm, there is little reduction in strength in an actual product, and each physical property can be guaranteed to 70% or more with respect to an unfoamed product at an expansion ratio of 1.3 times or less. That is, the foamed molded product having the maximum cell diameter in the range of 0.5 to 20 μm has both weight reduction and strength due to fine foaming.

Here, the dynamic viscoelasticity value is one of the indexes for evaluating the viscosity and elasticity of the resin, and one end side of the sample is fixed using a dynamic viscoelasticity measuring device. While the other end side is subjected to periodic vibration deformation by twisting a predetermined amount, the twisting load is released, and the obtained angle δ is measured.
It can be obtained as an δ (at 10 HZ).

This dynamic viscoelasticity value (tan δ, 10 HZ
Above), that is, the predetermined range of the dynamic viscoelasticity value when starting and ending the foaming of the thermoplastic resin is 0.07 to 0 when carbon dioxide is used as the subcritical or supercritical fluid. It can be 1. If the dynamic viscoelasticity value at the time of starting and ending the foaming of the thermoplastic resin is too small, the molecular chain of the thermoplastic resin remains solid, and it is difficult for the cells to grow and foaming becomes insufficient, resulting in a foamed molded product. It will be difficult to sufficiently reduce the weight. On the other hand, if the dynamic viscoelasticity value at the time of starting and ending the foaming of the thermoplastic resin is too large, the molecular chains of the thermoplastic resin become too loose, and the cell growth rate increases and the maximum cell diameter of the bubbles becomes excessive. Therefore, this maximum cell diameter portion may become a starting point of internal defects in strength and cause a decrease in strength.

The above-mentioned dynamic viscoelasticity value is unique to each resin material and has a correlation with the resin temperature. For example, PP,
As shown in FIG. 2, the relationship between the resin temperature and the dynamic viscoelasticity value of PA6 and PA6GF30 is shown in FIG.
ASF, model B3WG6) has a resin temperature of 210 to 220 ° C. or 60 to 80 ° C. and PA6 (Ube Industries,
In model 1013NB), 210-220 ° C, 80-95
At a resin temperature of 50 ° C or 50 to 55 ° C, and 80 to 15 for PP (manufactured by Grand Polymer Co., model TSOP-GP5).
The dynamic viscoelasticity value tan δ (1
0HZ) falls within the range of 0.07-0.10.

Therefore, in the foaming step, the foaming of the thermoplastic resin is started and ended within a predetermined resin temperature range that provides a predetermined dynamic viscoelasticity value range depending on the resin material used. It should be noted that the start of foaming of the thermoplastic resin means that bubble nuclei start to be generated, and the end of foaming means a state in which generation of bubbles is completed and cell growth is stopped.

Here, in the conventional foam molding method in which the resin temperature at the time of foaming the thermoplastic resin is not controlled as in the present invention, in the mold cooling process after foaming the thermoplastic resin, the foam molded article is cooled. There is a temperature distribution in the plate thickness direction, and cell growth is likely to proceed in the central portion of the inner layer, which is harder to cool than the surface layer portion in contact with the mold surface. Therefore, regardless of the presence or absence of the skin solid layer (the unfoamed portion of the surface layer in contact with the molding die surface) for both small and large articles, the foamed articles obtained by the conventional foaming method have a cell diameter in the center of the inner layer. Was being expanded. Moreover, since the cell diameter distribution based on the difference in the cell growth degree generally differs depending on the state and type of the material, there is no choice but to try it by trial and error in the absence of specific guidelines. It was difficult to control to the application level.

In this respect, in the method for foam-molding a thermoplastic resin of the present invention, the dynamic viscoelasticity value of the thermoplastic resin is within the predetermined range by controlling the resin temperature of the thermoplastic resin in the foaming step. At times, foaming of the thermoplastic resin is started and ended. That is, when the resin temperature of the thermoplastic resin is within a specific range, the foaming of the thermoplastic resin is started and ended. Therefore, it is possible to suppress the expansion of the foamed cell diameter in the center portion of the inner layer based on the temperature distribution in the plate thickness direction during the mold cooling process, and it is possible to reliably manage the maximum cell diameter.

After the foaming step is completed in this way, a demolding step of demolding the foamed molded product from the molding die is carried out.

At this time, depending on the demolding conditions (resin temperature, etc.), there are some resin materials in which cell growth occurs even after demolding and the foamed cell diameter increases, so that there is no specific guideline. It becomes difficult to control the cell diameter.

Therefore, in the demolding step, it is preferable that the foamed molded article is demolded from the molding die when the dynamic viscoelasticity value is out of the predetermined range. By doing so, expansion of the foamed cell diameter due to cell growth after demolding can be reliably suppressed, so that the maximum cell diameter can be managed easily and reliably.

Further, in the mold cooling process in the molding die, in addition to the temperature difference in the thickness direction of the foam molding as described above, the vicinity of the gate position for supplying the resin material into the molding die and this gate. A temperature difference due to a resin flow time difference or the like also occurs between the position away from the position and the position. In particular, such large temperature difference in resin flow is likely to occur in a large article or a complex shaped article. For this reason, it becomes difficult to reliably miniaturize the maximum cell diameter of the entire foam-molded article, especially in large articles and articles with complicated shapes.

Therefore, it is preferable to control the resin temperature in the foaming step in the entire area of the molding die. That is, it is preferable to start and end the foaming of the thermoplastic resin while controlling the whole thermoplastic resin filled in the mold so as to be in the predetermined resin temperature range as described above. By doing so, it becomes possible to suppress the expansion of the foamed cell diameter and reliably manage the maximum cell diameter in the entire foamed molded product obtained.

The following three concrete methods for controlling the resin temperature at this time are exemplified.

1) The first stage mold is cooled by circulating a temperature control medium, which has been set to a predetermined temperature in advance so that the mold temperature of the mold is within the predetermined resin temperature range, in the cooling passage of the mold. The mold temperature of the molding die is set and controlled within the predetermined resin temperature range. Then, after the thermoplastic resin filled in the molding die has reached the temperature range over the entire region, the thermoplastic resin is expanded by a predetermined amount so as to have a predetermined expansion ratio. It starts and ends.
After that, the temperature of the temperature control medium is switched to further cool the mold (second stage mold cooling) so that the mold temperature falls outside the predetermined resin temperature range and the temperature of the entire foamed molded product falls to the predetermined temperature. After the resin temperature is out of the range, the mold is largely opened to remove the foamed molded product.

2) Similar to 1) above, after the foaming of the thermoplastic resin is started and completed by cooling the first mold, the mold is cooled in the second mold so that the temperature of the entire foamed molded product is the above predetermined resin. When the temperature falls outside the temperature range, the foamed molded product is once released. Then, the foamed molded body is set in another cooling mold that can be cooled by a temperature control medium having a lower temperature, and the foamed molded body is cooled until the shrinkage amount and the like are stabilized, and then released from the mold. If the foamed molded product once released from the mold is set again in another cooling mold, it can be produced without changing the mold temperature, which is advantageous in terms of cycle time.

3) A temperature control medium preset at a predetermined temperature is set in the cooling passage of the mold so that the mold temperature of the mold is lower than the lower limit of the predetermined resin temperature range within about 10 ° C. By circulating the mold, the mold is cooled and the mold temperature is set and controlled to a temperature lower than the lower limit of the predetermined resin temperature range within about 10 ° C. Then, by controlling the cooling time in this cooling process, a predetermined expansion ratio is obtained when the highest temperature portion (the center portion in the plate thickness direction) of the resin in the molding die falls within the predetermined resin temperature range. By opening the mold by a predetermined amount, the foaming of the thermoplastic resin starts and ends. Then, after the mold temperature of the mold and the temperature of the entire foamed molded product become lower than the lower limit of the predetermined resin temperature range within about 10 ° C., the same method as in 1) or 2) above. The foamed molded product is demolded with. In this method, the mold temperature of the molding die is drastically lowered as compared with the above 1) and 2), so that the obtained foamed molded article has a thicker skin layer (unfoamed portion) of the surface layer and the total cooling rate. The time can be shortened.

Further, the expansion of the foamed cell diameter in the foamed molded product also occurs by adopting a hot runner. Normally, the resin material injected from the nozzle passes through the sprue and runner and through the gate and is filled into the cavity of the mold.However, a hot runner is used to improve the resin yield and shorten the molding cycle. There is a case. In addition,
The hot runner is a structure in which a sprue or a runner portion is heated so that the resin material in this portion is always kept in a molten state. In particular, a large number of articles or a complicated article often require a large number of gates with hot runners. Since the resin material is always kept in the molten state in the hot runner portion as described above, the gas-dissolved resin always remains in this hot runner portion. Therefore, when the pressure in the mold is released, the resin in the hot runner portion foams and the cell diameter also grows large. The foamed resin in the hot runner portion is filled in the molding die in the next injection shot and mixed into the product, so that when the hot runner is adopted, it is extremely difficult to control the maximum cell diameter.

Therefore, when a hot runner is adopted and the thermoplastic resin is filled into the mold through the hot runner in the filling step, a hot runner having opening and closing means at the inlet and the gate is used. Adopted, at least when the mold is opened, in order to maintain the pressure in the hot runner, it is opened when the thermoplastic resin is filled and at least closed when the mold is opened. It is preferable that the hot runner is provided with an opening / closing means that is controlled to be opened and closed. It should be noted that the opening / closing means may be closed at any time after the thermoplastic resin has been filled in the molding die, or may be closed immediately after the filling. With this configuration, by opening the opening / closing means in the filling step,
It becomes possible to inject and fill the resin material into the mold through the hot runner, and by closing the opening means in the foaming step and the mold releasing step, that is, when the mold is opened, that is, the molding is performed. Even when the pressure in the mold is released, the pressure in the hot runner can be maintained at a predetermined pressure at which the resin does not foam. By doing so, it is possible to reliably prevent the resin material for the next injection shot remaining in the hot runner from foaming. Therefore, even when the hot runner is adopted, it is possible to reliably suppress the expansion of the foam cells and reliably manage the maximum cell diameter.

[0046]

EXAMPLES Examples of the thermoplastic resin foam molding method of the present invention will be specifically described below.

Example 1 The foam molding apparatus shown in FIG.
A mold 1 having a predetermined cavity shape, and an injection barrel 2 for supplying a molten resin into the cavity of the mold 1.
A hot runner 3 disposed between the injection barrel 2 and the molding die 1 and having opening and closing means at the inlet and the gate, and a cooling medium (oil) in a cooling passage (not shown) of the molding die 1. ), A gas supply device 5 for supplying carbon dioxide as a supercritical gas into the injection barrel 2 and the cavity of the mold 1, and a control means 6 for controlling opening / closing of the hot runner 3. It has and.

As shown in FIG. 4, the hot runner 3 includes a hot runner block 31, an inlet block 32 connected to the injection barrel 2, and a plurality of hot runner blocks connected to the molding die 1 and communicating with the inside of the cavity. And an exit gate 33 of Hot runner block 3
1, the inlet block 32 and each outlet date 33 are provided with a heater (not shown).

The inlet block 32 is provided with a rotary valve 32a capable of opening / closing the communication between the injection barrel 2 and the inlet block 32. In addition, each exit gate 33
Respectively include rod type valves (not shown) capable of opening / closing the communication between the cavity of the mold 1 and each outlet gate 33. The rotary valve 32a provided in the inlet block 32 and the rod type valve provided in each of the outlet gates 33 constitute an opening / closing means. And the rotary valve 3 as this opening / closing means
2a and each rod type valve are controlled by the control device 6 as described above.
It is opened when the thermoplastic resin is filled in the filling step described later, and is closed to maintain the pressure in the hot runner 3 when the mold 1 is opened in the foaming step and the demolding step described later. The opening and closing is controlled so that

Using the foam molding apparatus having the above structure, PA6 (manufactured by Ube Industries, model 1013NB) was used as the thermoplastic resin.
Was adopted and carbon dioxide was adopted as a supercritical fluid, and foam molding was performed as follows.

As described above, PA6 is 80 to 9
Within the predetermined resin temperature range of 5 ° C., the dynamic viscoelasticity value (tan δ, 10 HZ) in the solid state is 0.0
It is within the range of 7 to 0.1 (see FIG. 2).

(Filling Step) PA6 is supplied into the injection barrel 2 to form a molten resin, and carbon dioxide as a supercritical fluid is supplied from the gas supply device 5 into the injection barrel 2 to supply carbon dioxide to the molten resin. Was sufficiently kneaded and dissolved. At this time, the pressure in the injection barrel 2 was 20 MPa, and the resin temperature in the injection barrel 2 was 270 ° C. The resin temperature can be set to about 260 to 290 ° C. Further, the gas content rate of carbon dioxide with respect to the molten resin was set to 2 wt%.

On the other hand, in order to suppress the foaming of the thermoplastic resin filled in the cavity, the mold 1 is closed, and the gas supply device 5 enters the cavity as a supercritical fluid in the cavity of the mold 1. Carbon was supplied so that the pressure inside the cavity was 10 MPa.

At the same time as the control device 6 opens the rotary valve 32a and each rod-type valve as the opening / closing means, at the same time, the supercritical fluid is introduced from the injection barrel 2 into the cavity of the mold 1 through the hot runner 3. The melted molten resin was injected and filled.

The plate thickness in the cavity of the mold 1 in the mold closed state (plate thickness at the initial stage of molding) is 3.0 mm.

(Foaming step) <First cooling> Cooling of the mold 1 from the cooling device 4 so that the mold temperature of the mold 1 and the resin temperature in the cavity are within the predetermined resin temperature range (80 to 95 ° C.). The molded product was cooled for 30 seconds while the first stage mold cooling of the mold 1 was performed with the temperature control medium of 85 ° C. circulated in the passage.

Thereby, the mold temperature of the mold 1 and the mold 1
The entire molten resin filled in the cavity was heated to 85 ° C., which is within the predetermined resin temperature range. At this time, P
A6 dynamic viscoelasticity value (tan δ, 10
HZ) is 0.09.

Then, the controller 6 closed the rotary valve 32a as an opening / closing means and each rod type valve, and at the same time, opened the molding die 1 by a predetermined amount so as to obtain a predetermined expansion ratio. By this mold opening, the internal pressure of the cavity was instantaneously reduced to atmospheric pressure, and when the resin in the cavity started to foam, the cells grew to the target magnification within a few seconds, the resin foaming ended, and it was cooled and solidified. . The expansion ratio at this time was 1.2 times.

(Demolding Step) <Second Cooling> The mold temperature of the mold 1 and the resin temperature of the foamed molded product in the cavity are set to the above predetermined resin temperature range (50 to 5).
5 [deg.] C., 80 to 95 [deg.] C.), the temperature of the temperature control medium in the cooling device 4 is switched, and the molding die 1 is cooled with the temperature control medium of 45 [deg.] C. which is circulated in the cooling passage of the molding die 1. The molded product was cooled for 15 seconds during the second stage mold cooling.
As a result, the mold temperature of the mold 1 and the temperature of the entire foam-molded body in the cavity of the mold 1 were set to 45 ° C., which is lower than the predetermined resin temperature range.

Then, the mold 1 was largely opened to remove the foamed molded product. The maximum cell diameter of the obtained foamed molded product was 8 μm.

Also in this demolding step, the rotary valve 32a as the opening / closing means and each rod type valve were closed, and the pressure in the hot runner 3 was kept at a predetermined pressure.

The final thickness of the obtained foamed molded product was 3.6 mm, and the thickness of the skin layer was 0.05-.
It was 0.1 mm.

As described above, in this example, the dynamic viscoelasticity value (tan δ, 10 HZ) of PA6 in the solid state at a temperature lower than the melting point of PA6 as the thermoplastic resin is 0.07 to 0. When the temperature was 80 to 95 ° C., which was within the range of 0.1, the maximum cell diameter in the obtained foamed molded product could be 8 μm by starting and ending the foaming.

Therefore, according to this example, it was possible to obtain a foamed molded product having both weight reduction and strength due to fine foaming.

Further, in the present embodiment, in the foaming step, the foaming of the thermoplastic resin is started and ended when the resin temperature is within the specific range. Therefore, it is possible to suppress the expansion of the foamed cell diameter in the center portion of the inner layer based on the temperature distribution in the plate thickness direction during the mold cooling process, and it is possible to reliably manage the maximum cell diameter.

Furthermore, in the present embodiment, in the demolding step,
Since the foam molded article is demolded when the dynamic viscoelasticity value deviates from the predetermined range, it is possible to reliably suppress the expansion of the foam cell diameter due to cell growth after demolding. Easy and reliable management of cell diameter.

In addition, in this embodiment, in the foaming step,
The resin temperature is controlled in the entire area of the molding die 1, and the thermoplastic resin filled in the molding die 1 is controlled so as to be in the predetermined resin temperature range as described above. The foaming is started and ended. That is, the first stage mold cooling is performed by circulating the temperature control medium, which has been set to a predetermined temperature in advance so that the mold temperature of the mold 1 falls within the predetermined resin temperature range, in the cooling passage of the mold 1. The mold temperature of the molding die 1 is set and controlled within the above-mentioned predetermined resin temperature range. Then, after the thermoplastic resin filled in the molding die 1 reaches the temperature range over the entire area, the mold is opened by a predetermined amount so as to have a predetermined expansion ratio, thereby foaming the thermoplastic resin. Start and end, then
The temperature of the temperature control medium is switched to further cool the molding die 1 (second-stage mold cooling) so that the molding temperature of the molding die 1 falls outside the predetermined resin temperature range, and the temperature of the entire foamed molded product falls above the predetermined temperature. After the resin temperature is out of the range, the mold is largely opened to remove the foamed molded product. For this reason, in the entire foam-molded product obtained, it is possible to suppress expansion of the foam cell diameter and reliably manage the maximum cell diameter.

Further, in this embodiment, when the mold 1 is opened in the foaming step and the mold releasing step, the controller 6 controls the rotary valve 32a as the opening / closing means and each rod type valve. By closing each of them, the pressure inside the hot runner 3 is maintained at a predetermined pressure. Therefore, even when the molding die 1 is opened, that is, when the pressure in the molding die 1 is released, the pressure in the hot runner 3 can be maintained at a predetermined pressure capable of suppressing foaming of the resin. Therefore, it is possible to reliably prevent the resin material for the next injection shot remaining in the hot runner 3 from foaming. Therefore, even when the hot runner 3 is used, it is possible to reliably suppress the expansion of the foam cells and reliably manage the maximum cell diameter.

Example 2 Using the same foam molding apparatus as in Example 1 above, PP (Grand Polymer Co., model TSOP-GP5) was adopted as the thermoplastic resin, and carbon dioxide was adopted as the supercritical fluid. Then, foam molding was performed as follows.

As described above, this PP is 80-
Within the predetermined resin temperature range of 150 ° C., the dynamic viscoelasticity value (tan δ, 10 HZ) in the solid state falls within the predetermined range of 0.07 to 0.1 (see FIG. 2).

(Filling Step) PP is supplied into the injection barrel 2 to form a molten resin, and carbon dioxide as a supercritical fluid is supplied from the gas supply device 5 into the injection barrel 2 to supply carbon dioxide to the molten resin. Was sufficiently kneaded and dissolved.
At this time, the pressure in the injection barrel 2 was 15 MPa, and the resin temperature in the injection barrel 2 was 220 ° C. The resin temperature can be set to about 200 to 230 ° C.
Also, the gas content of carbon dioxide with respect to the molten resin is 1w.
It was set to t%.

On the other hand, in order to suppress the foaming of the thermoplastic resin filled in the cavity, the mold 1 is closed, and the gas supply device 5 supplies carbon dioxide as a supercritical fluid into the cavity of the mold 1. Carbon was supplied so that the pressure inside the cavity was 10 MPa.

Then, the rotary valve 32a as an opening / closing means and each rod type valve are respectively opened by the control device 6, and at the same time, the supercritical fluid is introduced from the injection barrel 2 into the cavity of the mold 1 through the hot runner 3. The melted molten resin was injected and filled.

The plate thickness in the cavity of the mold 1 in the mold closed state (plate thickness at the initial stage of molding) is 3.0 mm.

(Foaming Step) <First Cooling> Cooling of the mold 1 from the cooling device 4 so that the mold temperature of the mold 1 and the resin temperature in the cavity are within the predetermined resin temperature range (80 to 150 ° C.). The molded product was cooled for 15 seconds while the first stage mold of the mold 1 was cooled with the temperature control medium of 90 ° C. circulated in the passage.

As a result, the mold temperature of the mold 1 and the mold 1
The entire molten resin filled in the cavity was heated to 90 ° C., which is within the predetermined resin temperature range. At this time, P
Dynamic viscoelasticity value of P in solid state (tan δ, 10H
At the time of Z) is 0.08.

Then, the controller 6 closed the rotary valve 32a as an opening / closing means and each rod type valve, and at the same time, opened the molding die 1 by a predetermined amount so as to obtain a predetermined expansion ratio. By this mold opening, the internal pressure of the cavity was instantaneously reduced to atmospheric pressure, and when the resin in the cavity started to foam, the cells grew to the target magnification within a few seconds, the resin foaming ended, and it was cooled and solidified. . The expansion ratio at this time was 1.3 times.

(Demolding Step) <Second Cooling> The mold temperature of the mold 1 and the resin temperature of the foamed molded product in the cavity are set to the above-mentioned predetermined resin temperature range (80 to 1).
The temperature of the temperature control medium in the cooling device 4 is switched so as to be outside the temperature of 50 ° C.), and the temperature control medium of 70 ° C. circulated from the cooling device 4 into the cooling passage of the molding die 1 is used for the second stage of the molding die 1. The molded product was cooled for 10 seconds while performing mold cooling. The foamed molded product was once released from the mold when the temperature of the molding die 1 and the entire foamed molded product was 70 ° C., which was lower than the above-mentioned predetermined resin temperature range.
Then, the foamed molded body is set in another cooling mold (not shown), and further cooled for 15 seconds with a temperature control medium having a low temperature of 40 ° C. so that the amount of shrinkage of the foamed molded body is stabilized. The mold temperature and the temperature of the entire foamed molded product were cooled to 40 ° C., and then the mold was released. The maximum cell diameter of the obtained foamed molded product was 5 μm.

Also in this demolding step, the rotary valve 32a as the opening / closing means and each rod type valve were closed, and the pressure inside the hot runner 3 was kept at a predetermined pressure.

The final thickness of the obtained foamed molded product was 3.9 mm, and the thickness of the skin layer was from 0.05 to
It was 0.1 mm.

In this embodiment, in addition to the same effects as in the first embodiment, the foamed molded product once released in the second stage mold cooling is set in another cooling mold. Also, there is an effect that the total cycle time can be shortened.

Example 3 Using the same foam molding apparatus as in Example 1 above, PA6 (manufactured by Ube Industries, model 1013NB) was used as the thermoplastic resin, and carbon dioxide was used as the supercritical fluid. Foam molding was performed as follows.

As described above, this PA6 has 50
Within the predetermined resin temperature range of ˜55 ° C., the dynamic viscoelasticity value (tan δ, 10 HZ) in the solid state falls within the predetermined range of 0.07 to 0.1 (see FIG. 2).

(Filling Step) PA6 is supplied into the injection barrel 2 to form a molten resin, and carbon dioxide as a supercritical fluid is supplied from the gas supply device 5 into the injection barrel 2 to supply carbon dioxide to the molten resin. Was sufficiently kneaded and dissolved. At this time, the pressure in the injection barrel 2 was 20 MPa, and the resin temperature in the injection barrel 2 was 270 ° C. The resin temperature can be set to about 260 to 290 ° C. Further, the gas content rate of carbon dioxide with respect to the molten resin was set to 2 wt%.

On the other hand, in order to suppress the foaming of the thermoplastic resin filled in the cavity, the mold 1 is closed, and the gas supply device 5 supplies carbon dioxide as a supercritical fluid into the cavity of the mold 1. Carbon was supplied so that the pressure inside the cavity was 10 MPa.

Then, the rotary valve 32a as an opening / closing means and each rod type valve are opened by the control device 6, and at the same time, the supercritical fluid is introduced from the injection barrel 2 into the cavity of the mold 1 through the hot runner 3. The melted molten resin was injected and filled.

The plate thickness in the cavity of the mold 1 in the mold closed state (plate thickness at the initial stage of molding) is 3.0 mm.

(Foaming Step) <First Cooling> The mold temperature of the molding die 1 and the resin temperature in the cavity are set within the predetermined resin temperature range (50 to 55 ° C.), and finally the mold of the molding die 1 is formed. The temperature and the resin temperature in the cavity from the lower limit (50 ° C) of this resin temperature range to 1
25 seconds while performing the first stage mold cooling of the mold 1 with the temperature control medium of 40 ° C. which is circulated from the cooling device 4 into the cooling passage of the mold 1 so as to be 40 ° C. which is 0 ° C. lower temperature. The molded product was cooled.

By selecting this cooling time, the mold temperature of the molding die 1 and the resin temperature of the highest temperature portion (in the central portion of the plate thickness) of the molten resin filled in the cavity of the molding die 1 are 52 to 53 ° C.
I tried to become. At this time, the dynamic viscoelasticity value (tan δ, 10 HZ) of PA6 in the solid state is 0.0.
8

Then, by the control device 6, the rotary valve 32a as the opening / closing means and each rod type valve were respectively closed, and at the same time, the molding die 1 was opened by a predetermined amount so as to obtain a predetermined expansion ratio. By this mold opening, the internal pressure of the cavity was instantaneously reduced to atmospheric pressure, and when the resin in the cavity started to foam, the cells grew to the target magnification within a few seconds, the resin foaming ended, and it was cooled and solidified. . The expansion ratio at this time was 1.2 times.

(Die-Molding Step) <Second Cooling> The mold temperature of the mold 1 and the resin temperature of the foam-molded body in the cavity are set in the predetermined resin temperature range (50 to 5).
5 ° C.), which is 10 ° C. lower than the lower limit of 40 ° C., with the temperature control medium kept at 40 ° C. with the temperature control medium flowing from the cooling device 4 into the cooling passage of the molding die 1. The molded product was cooled for 10 seconds while the second stage mold cooling of 1 was performed.
As a result, the mold temperature of the mold 1 and the temperature of the entire foam molded product are 40 ° C., which is 10 ° C. lower than the lower limit of the predetermined resin temperature range.
And

Then, the molded body 1 was largely opened, and the foamed molded body was released from the mold. The maximum cell diameter of the obtained foamed molded product was 5 μm.

Also in this demolding step, the rotary valve 32a as the opening / closing means and each rod type valve were closed, and the pressure inside the hot runner 3 was kept at a predetermined pressure.

The final thickness of the obtained foamed molded product was 3.6 mm, and the thickness of the skin layer was 0.25 to 0.3 mm, which was 0.2 mm larger than that of Example 1. there were.

In this embodiment, in addition to the same effects as the first embodiment, there is an effect that the total cooling time can be shortened.

[0096]

As described in detail above, in the method for foam molding a thermoplastic resin of the present invention, when the dynamic viscoelasticity value in the solid state below the melting point of the thermoplastic resin is within a predetermined range, the thermoplastic resin By starting and ending the foaming of the resin, the resulting foamed molded article can be finely foamed, and the maximum cell diameter of the cells can be kept within a specific range. Therefore, according to the method of the present invention, it is possible to obtain a foamed molded product having both weight reduction and strength due to fine foaming.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a dynamic viscoelasticity value and a foam maximum cell diameter.

FIG. 2 is a diagram showing a relationship between a resin temperature and a dynamic viscoelasticity value.

FIG. 3 is a cross-sectional view showing a schematic configuration of a foam molding apparatus used in the thermoplastic resin foam molding method of the present embodiment.

FIG. 4 is a perspective view showing a hot runner constituting the foam molding apparatus.

[Explanation of symbols]

1 ... Mold 2 ... Injection barrel 3 ... Hot runner 4 ... Cooling device 5 ... Gas supply device 6 ... Control device 32a ... Rotary valve (opening / closing means)

Continued front page    F-term (reference) 4F206 AA29 AB02 AG20 AR02 AR06                       AR12 AR20 JA04 JF04 JM02                       JN11 JN41 JP15 JQ81

Claims (5)

[Claims] 1. A method of foaming a thermoplastic resin in which a thermoplastic resin mixed with a subcritical or supercritical fluid is foamed in a molding die, wherein the prepressurized to a predetermined pressure by the subcritical or supercritical fluid. In the molding die, a filling step of filling the thermoplastic resin mixed with the subcritical or supercritical fluid, and when the dynamic viscoelasticity value in the solid state below the melting point of the thermoplastic resin is within a predetermined range In, the foaming step of lowering the pressure in the mold to start foaming of the thermoplastic resin, and ending the foaming to obtain a foamed molded article, in order. Foam molding method. 2. The subcritical or supercritical fluid is carbon dioxide, and the predetermined range of the dynamic viscoelasticity value is 0.0.
It is 7-0.1, The foaming molding method of the thermoplastic resin of Claim 1 characterized by the above-mentioned. 3. After the foaming step, a demolding step of demolding the foam molded article from the molding die when the dynamic viscoelasticity value deviates from the predetermined range is performed. Item 3. A method of foaming a thermoplastic resin according to Item 1 or 2. 4. The thermoplastic resin is filled in the mold through a hot runner having opening and closing means at the inlet and the gate in the filling step, and the opening and closing means opens at least the mold. In order to maintain the pressure in the hot runner, the opening and closing control is performed so that it is opened when the thermoplastic resin is filled and at least closed when the mold is opened. The foam molding method of the thermoplastic resin according to claim 1, 2, or 3. 5. A foamed molded article obtained by foaming a thermoplastic resin mixed with a supercritical fluid in a molding die, wherein the maximum cell diameter is 0.5 to 20 μm. Molded body.